As you can see, a fartlek is a continuous run with varying speeds, while interval training sometimes allows you to take a brief rest. Tempo runs involve a warm-up and cool-down with your threshold speed mixed in the middle.
Fartlek vs. Interval
Both fartlek and interval training methods aim to improve speed and endurance but differ in structure and execution. Fartlek is more spontaneous and flexible, allowing runners to adjust their intensity based on instinct and environmental cues.
It's less about timing and more about feeling, making it a playful and adaptable approach to speedwork.